Powder filling method and arrangement therefor

ABSTRACT

A powder box, an arrangement for a powder box comprising an insert and a method for filling powder into a cavity formed in a die. Gas is supplied to a powder box, which is movable toward and away from a position just above the cavity. The gas is supplied through a permeable plate, which is arranged on at least one insert and which faces the interior of the powder box, so that particles of the powder in the powder box are movable relative to each other. The fluidisation of the powder shortens the filling time and results in an even particle size distribution in the cavity.

FIELD OF THE INVENTION

The present invention relates to a powder filling method and anarrangement therefor. Specifically the invention concerns a powder boxarrangement for filling powder into a cavity formed in a die.

BACKGROUND OF THE INVENTION

In conventional powder filling methods, powder in a powder box orfilling shoe is transferred into a cavity formed in a die when thepowder box is brought to a position just above the cavity. However, whenentrapped air in the cavity is driven away by the powder, lightparticles whirl up while heavy particles drop quickly so that unevennessin particle size distribution occurs in the cavity. As a result, thereis a risk that a sintered powder metallurgical component made from thepowder will get a non-uniform density distribution and, as aconsequence, less accurate dimensions as well as non-uniformalmechanical strength and magnetic properties.

A method eliminating some of the problems with conventional filling isdisclosed in U.S. Pat. No. 5,881,357. This patent discloses a powder boxhaving at least one pipe disposed within the powder box. Each pipe whichis fastened in the wall of the powder box has a plurality of holes forsupplying gas into the powder in the powder box.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a powder boxarrangement which eliminates the use of pipes and problems originatingfrom the use thereof.

A second object is to provide an arrangement that can easily be adaptedto suit any powder box.

A third object of the invention is to provide a powder box and a methodfor filling powder in a cavity uniformly and in a short time period.

A forth object of the invention is to provide a powder box and a fillingmethod that secures good flowability of the powder in a verticaldirection.

These objects as well as other objects that will be apparent from thedescription below, have now been obtained according to the presentinvention by providing a powder box according to claim 1, an arrangementfor a powder box comprising an insert according to claim 4 and a methodfor filling powder into a cavity according to claim 8.

SUMMARY OF THE INVENTION

In brief the arrangement according to the invention concerns a powderbox having arranged therein at least one insert comprising a permeableplate, a gas impermeable backing and a spacing therebetween. The spacingis connectable to a gas supply through at least one hose.

The invention also comprises a method for filling powder into a cavityformed in a die comprising the steps of:

a) supplying gas to a powder box, which is movable horizontally towardand away from a position just above the cavity, whereby the gas issupplied through a permeable plate which is arranged on at least oneinsert and which faces the interior of the powder box so that particlesof the powder in the powder box are movable relative to each other; and

b) moving the powder box to the position just above the cavity so thatthe powder in the powder box enters the cavity at least by gravity.

Finally the invention also concerns the insert as defined above.

DETAILED DESCRIPTION OF THE INVENTION

The key features of the present invention is the insert and thearrangement thereof in the powder box.

The configuration of the insert is decided by the man skilled in the artin view of the configuration of the die cavity and the powder box.Normally the insert is an essentially plane surface although othershapes may be used.

The permeable plate preferably consists of a porous material such as apolymer, metallic, or a ceramic material or a mixture thereof. Thelargest pore of the permeable plate should be smaller than the smallestparticle of the powder to prevent the powder from clogging the pores.

Suitable materials for the backing are metals and polymers such aspolyamides.

The inserts which may be prepared with an optional relation betweenheight and length, are arranged to partially or totally cover a sidewall of the powder box. The insert(s) may also be arranged so as toincline towards the bottom of the powder box or may be arranged on acover covering the powder box. One insert is sufficient for simplecavity geoemtries.

A preferred embodiment of the powder box according to the inventioncomprises two inserts arranged on opposing sides of the powder box sothat they are positioned on two opposing sides of the cavity when thepowder box is positioned just above the cavity in the die.

The powder box is preferably covered with a cover to avoid spillage,contamination and to minimise dusting. The cover is preferably fittedwith an exhaust hole to prevent the build up of the fluidising media,such as air or gas.

It can easily be realised that the insert according to the invention canbe adapted to suit any powder box and any cavity configuration.

The powder filling arrangement according to the present inventionimproves the filling capacity by releasing air that becomes entrappedduring the filling of the powder into the cavity.

Furthermore, and in contrast to the arrangement disclosed in the U.S.Pat. No. 5,881,357 which also concerns fluidised filling, the fillingarrangement according to the present invention improves the fillingcapacity by reducing the friction of the powder particles against thewalls of the powder box during the filling by using the inserts. Anotheradvantage in comparison with the arrangement known from this U.S. patentis that the inserts are arranged in the powder box in such a way thatthey do not obstruct the flow of the powder during the filling of thepowder into the cavity as is the case with the pipes in the knownapparatus. This is especially important as every obstruction for thepowder flow on the way to the cavity may cause a segregation of thepowder. Unexpectedly it has also been found that approximately the samefilling density can be obtained for cavities having quite differentsizes and that the fill density is independent of the speed of thepowder box. The arrangement for improving the filling capacity accordingto the present invention can also easily be adapted to a wide variety ofexisting powder boxes with simple fastening means, such as glue, screws,welding etc. Furthermore, the fill volume of a powder box having a givenvolume may be varied by adjusting the angle of inclination α whichshould be >0° C. as is described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described below with reference to theappended drawing showing a presently preferred embodiment.

FIG. 1 is a schematic drawing showing a movable fluidised powder boxwith two inserts.

FIG. 2 is a schematic drawing showing a) a front view and b) a side viewof an insert.

FIG. 3 is a table with results from a test using the powder boxaccording to the invention.

FIG. 4 is a chart comparing a conventional powder box withoutfluidisation with a powder box with fluidising inserts according to theinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

A powder box 2 for filling powder into a cavity 30 formed in a die 31according to the present invention is shown in FIG. 1. The powder box 2is connected to a flexible hose 3 for supply of gas to the interior ofthe powder box 2.

The powder box 2 is covered by a cover 4. The cover 4 is penetrated by apipe 5 which supply powder into the powder box 2. The cover 4 has anexhaust hole 1 for gas to prevent a pressure build up in the powder box2. The bottom 6 of the powder box 2 is open.

The powder box 2 has two inserts 20 arranged therein. The inserts 20 areattached to opposing sides of the walls 8 on the inside of the powderbox 2 by means of glue, screws, welding or the like.

The angle α of the inserts relative the bottom 6 of the powder box 2 isnormally between 30° and 90°. The length of the inserts 20 is decided bythe size of the cavity 30 to be filled.

The inserts 20 include a permeable plate 21 facing the interior of thepowder box 2, a gas impermeable backing or holder 22, and a spacing 23therebetween.

A detail view of the inserts are shown in FIG. 2. The porous plate 21,made of PPMD available from PIAB Sweden, is glued to the holder 22 madeof polyamide. A threaded hole 24 is located in the centre of the holder22 for connecting the spacing 23 to a gas source with a flexible hose 3.The hose 3 may also be glued or by other means fastened to the hole 24in the holder 22. The hose 3 penetrates the wall 8 of the powder box 2.

Referring again to FIG. 1 the powder box 2 is movable in a horizontaldirection A toward and away from a position just above the cavity 30 inthe die 31. Powder (having room temperature or higher) is suppliedintermittently through the pipe 5. Gas or air (having room temperatureor higher) is supplied to the powder box 2 when the box approaches thecavity 30. The gas is supplied from the gas source through the hose 3and into the spacing 23 from where the gas escapes into the powderthrough the permeable plate 21. The gas flow is set to such a value thatfluidisation of the powder particles in the powder bed 7 is initiated.The fluidisation makes the particles move relative to each other to anextent that causes visual bubbling of the powder.

The powder enters the cavity 30 when the powder box 2 is located abovethe cavity 30. Due to the fluidisation of the powder, the powder entersthe cavity 30 easily and smoothly without whirling up in the powder bed7, so that unevenness in particle size distribution in the cavity 30 isunlikely to occur.

The above method can be used for gravity, sequence as well as suctionfilling.

FIG. 3 shows a table with results from a test run where decreasing sizedcavities (cavity no 1-5) were filled with Distaloy AE® (an iron powderfrom Hoganas AB) with an increasing speed (test 1-test 6). The resultsshow that, within the studied region, the fill density is independent ofthe cavity volume.

FIG. 4 shows that the fillability index for the powder box withfluidising inserts according to the invention does not change with thespeed rate of the powder box as is the case for conventional powderboxes without fluidisation.

What is claimed is:
 1. A powder box (2) for filling powder into a cavityformed in a die, having arranged therein at least one insert (20)including a gas permeable plate (21), which faces the interior of thepowder box (2) and which is arranged at an angle α>0° relative to thebottom (6) of the powder box (2), a gas impermeable backing (22) and aspacing (23) therebetween, the spacing (23) being connectable to a gassupply through at least one hose (3).
 2. The powder box (2) according toclaim 1 wherein the angle α varies between 30 and 90°.
 3. The powder box(2) according to claim 1, having two inserts (20) positioned on opposingsides of the powder box (2).
 4. The powder box (2) according to claim 1,wherein the inserts (20) are attached to the walls (8) on the inside ofthe powder box (2) by means of glue, welding or screws.
 5. An insert(20) for a powder box (2) comprising a gas permeable plate (21), a gasimpermeable backing (22) and a spacing (23) therebetween, the spacing(23) being connectable to a gas supply.
 6. The insert (20) according toclaim 5, wherein the insert (20) is adjustable within the powder box(2).
 7. The insert (20) according to claim 5, wherein the largest poreof the gas permeable plate is smaller than the smallest particle of thepowder used.
 8. The insert (20) according to claim 5, wherein the gaspermeable plate (21) is of a polymer, metal or a ceramic material or amixture thereof.
 9. A method for filling powder into a cavity (30)formed in a die (31) comprising the steps of: a) supplying gas to apowder box (2), which is movable horizontally toward and away from aposition just above the cavity (30), whereby the gas is supplied througha permeable plate (21) which is arranged on at least one insert (20),whereby the plate faces the interior of the powder box (2) and isarranged at an angle α, which is >0° C., relative to the bottom (6) ofthe powder box (2) so that particles of the powder in the powder box (2)are movable relative to each other; and b) moving the powder box (2) tothe position just above the cavity (30) so that the powder in the powderbox (2) enters the cavity (30) at least by gravity.
 10. The methodaccording to claim 9, wherein the gas flow through the permeable plate(21) is set at a value that causes visual fluidisation of the powder.11. The powder box (2) according to claim 2, having two inserts (20)positioned on opposing sides of the powder box (2).
 12. The powder box(2) according to claim 2, wherein the inserts (20) are attached to thewalls (8) on the inside of the powder box (2) by means of glue, weldingor screws.
 13. The powder box (2) according to claim 3, wherein theinserts (20) are attached to the walls (8) on the inside of the powderbox (2) by means of glue, welding or screws.
 14. The powder box (2)according to claim 11, wherein the inserts (20) are attached to thewalls (8) on the inside of the powder box (2) by means of glue, weldingor screws.
 15. The insert (20) according to claim 6, wherein the largestpore of the gas permeable plate is smaller than the smallest particle ofthe powder used.
 16. The insert (20) according to claim 6, wherein thegas permeable plate (21) is of a polymer, metal or a ceramic material ora mixture thereof.
 17. The insert (20) according to claim 7, wherein thegas permeable plate (21) is of a polymer, metal or a ceramic material ora mixture thereof.
 18. The insert (20) according to claim 15, whereinthe gas permeable plate (21) is of a polymer, metal or a ceramicmaterial or a mixture thereof.